"Some years ago, the banks did change their practices to reduce the fees and we are still seeing the banks' profits [increase], so it hasn't made a huge difference to their bottom line."

Maurice Blackburn lawyer Andrew Watson says, if successful, any customer who has paid a late fee will have a right to compensation.

"We'll be alleging as we have in our earlier case against the ANZ that the late payment fees are penalties and excessive, and customers should get the difference between what they were charged and the true cost to the bank," he said .